Inclusion complexes of lanthanides (III) with modified cyclo-dextrins

Cyclo-dextrins are cyclic oligosaccharides which contain six (α, seven (β) or eight (γ) glucose units bound by α bonds. These molecules are bio-compatible, soluble in water and can incorporate organic substrates in their lipophilic cavity. The chemical modification of these natural cyclo-dextrins to give per-3,6-anhydro derived compounds changes radically the structure of the receptor and give a hydrophilic cavity. This inversion of the inclusion properties allows to obtain compounds able to bind the metallic ions. In order to reinforce the affinity of these molecules towards hard metallic cations, the residual hydroxyl groups (position 2) have been substituted by carboxy-methyl groups to obtain ACX (α) and BCX (β) cyclo-dextrins. The properties of these new compounds will be presented. The ACX and BCX ligands form mono-metallic and bimetallic complexes with lanthanides (III) in aqueous solution. The structure at the solid state of the compound [Lu2(ACX)(H2O)2] represents the first example of lanthanide-cyclo-dextrin inclusion complex. Indeed, each Lu(III) cation is encapsulated in the cavity and interacts both with carboxylate groups and the ether oxygens of the cyclo-dextrin. At last, the nuclear relaxation properties of the gadolinium(III) mono-metallic complexes will be discussed. (O.M.)